Moving trajectory calibration method and moving trajectory generation method

ABSTRACT

A moving trajectory calibration method is applied to receive a moving trajectory signal generated by a writing device while moving on a written plane and includes the following steps of: generating a first axial signal, a second axial signal and a third axial signal according to the moving trajectory signal by a detecting-calibration unit of an orientation calculation module, wherein the written plane is composed of the first axis and the second axis, and the third axis is perpendicular to the written plane; calibrating the first axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a first axial trajectory signal; and calibrating the second axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a second axial trajectory signal. In addition, a moving trajectory generation method is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

The non-provisional patent application claims priority to U.S.provisional patent application with Ser. No. 61/514,960 filed on Aug. 4,2011. This and all other extrinsic materials discussed herein areincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a moving trajectory calibration methodand a moving trajectory generation method.

2. Related Art

Recently, tremendous progress in miniaturization technology inelectronic circuits and components has greatly decreased the dimensionand weight of consumer electronic products and make them extremelypowerful, portable, and convenient. Due to the rapid development ofcomputer technology, human-computer interaction (HCI) techniques havebecome one of the indispensable tools in our daily life. Inparticularly, the hand writing through the HCI is an essential recordingor expressing method. Today, many handwriting-based HCI sensingtechnologies, which mainly include the electromagnetic, electric,ultrasonic, pressure, and optical sensing technologies, have beendisclosed.

However, the electromagnetic HCI sensing technology needs a battery withlarger capacity to provide a large power for generating theelectromagnetic field so as to detect and position the writing position,which is the pen-point of the writing device. Thus, this type writingdevice becomes heavier and is inconvenient in carrying. Besides, theelectric HCI sensing technology needs to cooperate with a specificelectrode paper and use the transmission and receiving electrodes of theelectrode paper to detect the moving trajectory of the writing device.Unfortunately, the electrode paper is very expensive, so this electricHCI sensing technology can not be popularized. The ultrasonic HCIsensing technology utilizes the arrival-time difference between theultrasonic signals and the triangulation location method to calculatethe writing trajectory coordinates of the pen-point of the writingdevice. Although the ultrasonic HCI sensing technology can preciselycapture the moving trajectory of the writing device on any 2-dimensionalplane, the writing range for receiving the ultrasonic waves with thecooperated receiving device is limited and very inconvenient. Thepressure HCI sensing technology has a limited writing range within thearea of the pressure sensing electronic board, so its operation is alsoinconvenient. The optical HCI sensing technology utilizes the opticalsensor of the optical mouse to sense the moving trajectory of thewriting device on a written plane. The sensing theory is similar to thatof the optical mouse, so that it is possible to simply convert themoving trajectory information into the operation signal of the cursorwithout developing additional application programming interface (API)software.

However, in all of the above sensing technologies, when writing deviceleaves the 2-dimensional written plane as it is lifted up or moved tonext stroke, the sensing devices still output the unnecessary sensingsignals to generate the incorrect moving trajectory.

Therefore, it is an important subject of the present invention toprovide a moving trajectory calibration method and a moving trajectorygeneration method that can correct the distorted moving trajectory asthe writing device is lifted up or moved to next stroke so as to obtainthe correct moving trajectory.

SUMMARY OF THE INVENTION

In view of the foregoing subject, an objective of the present inventionis to provide a moving trajectory calibration method and a movingtrajectory generation method that can detect handwriting signals andcorrect the distorted moving trajectory as the writing device is liftedup or moved to next stroke so as to obtain the correct movingtrajectory.

To achieve the above objective, the present invention discloses a movingtrajectory calibration method, which is applied to receive a movingtrajectory signal generated by a writing device while moving on awritten plane. The calibration method comprises the steps of: generatinga first axial signal, a second axial signal and a third axial signalaccording to the moving trajectory signal by a detecting-calibrationunit of an orientation calculation module, wherein the written plane iscomposed of the first axis and the second axis, and the third axis isperpendicular to the written plane; calibrating the first axial signalaccording to the third axial signal by the detecting-calibration unit,so as to generate a first axial trajectory signal; and calibrating thesecond axial signal according to the third axial signal by thedetecting-calibration unit, so as to generate a second axial trajectorysignal.

In one embodiment, the moving trajectory signal comprises an angularvelocity signal, an acceleration signal, a magnetic-field intensitysignal, a geomagnetic orientation signal, or their combinations in threeaxes with respect to a moving trajectory at different time points.

In one embodiment, the first axis, the second axis and the third axisare perpendicular to one another.

In one embodiment, the step of calibrating the first axial signalfurther comprises: when a variation of the third axial signal within atime interval exceeds a preset signal value, the detecting-calibrationunit zeros the first axial signal within the time interval.

In one embodiment, the step of calibrating the second axial signalfurther comprises: when a variation of the third axial signal within atime interval exceeds a preset signal value, the detecting-calibrationunit zeros the second axial signal within the time interval.

To achieve the above objective, the present invention also discloses amoving trajectory generation method, comprising the steps of: sensing amoving trajectory while a writing device moves on a written plane by amoving trajectory sensing module of the writing device, and generating amoving trajectory signal; generating a first axial signal, a secondaxial signal and a third axial signal according to the moving trajectorysignal by a detecting-calibration unit of an orientation calculationmodule, wherein the written plane is composed of the first axis and thesecond axis, and the third axis is perpendicular to the written plane;calibrating the first axial signal and the second axial signal accordingto the third axial signal by the detecting-calibration unit, so as togenerate a first axial trajectory signal and a second axial trajectorysignal, respectively; and displaying the calibrated moving trajectory bya display module according to the first axial trajectory signal and thesecond axial trajectory signal.

In one embodiment, the moving trajectory generation method furthercomprises the step of: generating a coordinate transformation matrixaccording to the angular velocity signals by an orientationtransformation unit of the orientation calculation module, andperforming the coordinate transformation to the acceleration signalsaccording to the coordinate transformation matrix.

In one embodiment, the orientation transformation unit integrates theangular velocity signals to obtain an orientation angle so as togenerate the coordinate transformation matrix, and transforms theacceleration signals with the coordinate transformation matrix so as totransform the acceleration signals from a body frame of the writingdevice to a local level frame.

In one embodiment, the moving trajectory generation method furthercomprises the step of: performing a gravity compensation to theacceleration signals in the local level frame by a gravity compensationunit of the orientation calculation module.

In one embodiment, the moving trajectory generation method furthercomprises the step of: performing a calculation to the first axialtrajectory signal and the second axial trajectory signal by a trajectorycalculation unit of the orientation calculation module.

In one embodiment, the written plane comprises a horizontal plane, avertical plane, or a slant plane.

As mentioned above, in the moving trajectory calibration method andmoving trajectory generation method of the invention, adetecting-calibration unit of an orientation calculation modulegenerates a first axial signal, a second axial signal and a third axialsignal according to the moving trajectory signal, while the writtenplane is composed of the first axis and the second axis, and the thirdaxis is perpendicular to the written plane. In addition, thedetecting-calibration unit calibrates the first axial signal and thesecond axial signal according to the third axial signal so as togenerate a first axial trajectory signal and a second axial trajectorysignal, respectively, and the display module then displays thecalibrated moving trajectory according to the first axial trajectorysignal and the second axial trajectory signal. Accordingly, the movingtrajectory calibration method and moving trajectory generation method ofthe invention can detect handwriting signals and correct the distortedmoving trajectory as the writing device is lifted up or moved to nextstroke so as to obtain the correct moving trajectory.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the detaileddescription and accompanying drawings, which are given for illustrationonly, and thus are not limitative of the present invention, and wherein:

FIG. 1A is a schematic diagram showing the circumstance of using awriting device to write on a written plane;

FIG. 1B is a block diagram of the writing device of FIG. 1A;

FIG. 1C is a flow chart of a moving trajectory calibration methodaccording to a preferred embodiment of the invention;

FIG. 2A is a schematic diagram showing the moving trajectory as usingthe writing device to write “4”;

FIG. 2B is a schematic diagram showing a modified moving trajectory byapplying the moving trajectory generation method of the invention to themoving trajectory of FIG. 2A;

FIG. 3A is a waveform diagram showing the acceleration signals in threeaxes from the moving trajectory signal;

FIG. 3B is a waveform diagram showing the acceleration signals in threeaxes of FIG. 3A processed by a coordinate transformation;

FIG. 3C is a waveform diagram showing the acceleration signals in threeaxes of FIG. 3B processed by a gravity compensation;

FIGS. 4A to 4C are waveform diagrams of a first axial signal, a secondaxial signal, and a third axial signal, respectively;

FIG. 5A is a flow chart of a moving trajectory generation methodaccording to a preferred embodiment of the invention;

FIG. 5B is a block diagram of the writing device applied to the movingtrajectory generation method of FIG. 5A;

FIG. 6A is a schematic diagram showing the moving trajectory as usingthe writing device to write “12”;

FIG. 6B is a schematic diagram showing a modified moving trajectory byapplying the moving trajectory generation method of the invention to themoving trajectory of FIG. 6A;

FIG. 7A is a schematic diagram showing the moving trajectory as usingthe writing device to write “86”; and

FIG. 7B is a schematic diagram showing a modified moving trajectory byapplying the moving trajectory generation method of the invention to themoving trajectory of FIG. 7A.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be apparent from the following detaileddescription, which proceeds with reference to the accompanying drawings,wherein the same references relate to the same elements.

FIG. 1A is a schematic diagram showing the circumstance of using awriting device 1 to write on a written plane P, and FIG. 1B is a blockdiagram of the writing device 1.

The writing device 1 includes an inertia sensing element for sensing theangle, orientation, and displacement of the writing device 1 in the3-dimensional space. In this case, the shape of the writing device 1 isa pen. Otherwise, the writing device can be made of other shapes ortypes such as a mouse.

Referring to FIG. 1B, the writing device 1 includes a moving trajectorysensing module. In addition, the writing device 1 may further include anorientation calculation module. In other embodiments, another processingdevice, such as a computer, may also include the orientation calculationmodule, and the signals generated by the moving trajectory sensingmodule can be transmitted to the orientation calculation module by wiresor wireless for further calculation.

The moving trajectory sensing module can sense a moving trajectory,which is generated as the writing device 1 moves in the 3-dimensionalspace, and generate a moving trajectory signal in real time. The movingtrajectory sensing module includes a multi-axis dynamic switch. Themoving trajectory can be a trajectory of a digit, a letter, a symbol, aline or any writing trajectory. In addition, the moving trajectorysignal may include the coordinate information, angular velocityinformation, gravity information, acceleration information,magnetic-field intensity information, geomagnetic orientationinformation, any other information, or their combinations in three axeswith respect to a moving trajectory at different time points. Besides,the written plane P may comprise a horizontal plane, a vertical plane,or a slant plane. In this embodiment, the written plane P is ahorizontal plane.

The moving trajectory sensing module includes, for example, a gyroscope,an accelerometer, a magnetometer or an electronic compass, or theircombinations. These devices can be a single axis or multiple axes (e.g.three axes), and the moving trajectory signal includes an angularvelocity signal, an acceleration signal, a magnetic-field intensitysignal, a geomagnetic orientation signal, or their combinations in threeaxes with respect to a moving trajectory at different time points. Inthis embodiment, the moving trajectory sensing module includes atriaxial gyroscope and a triaxial accelerometer for measuring thetriaxial angular velocity signals, the gravity g, and the triaxialacceleration signals. To be noted, the writing device 1 or anotherprocessing device may further include a calibration filtering unit (notshown), which can calibrate the signal generated by the inertia elementof the moving trajectory sensing module, such as the above-mentionedgyroscope, accelerometer, magnetometer or electronic compass, or theircombinations, and filter the noise of the inertia element or thecontaminated moving trajectory signal caused by unintentional handmotion (e.g. hand trembles) or other environmental interference.

Before performing the steps of the moving trajectory calibration methodof the embodiment, the moving trajectory signal (e.g. angular velocitysignals and the acceleration signals) must be preprocessed. As shown inFIG. 1B, the triaxial angular velocity signals are integrated by anorientation transformation unit of the orientation calculation module soas to obtain an orientation angle of the writing device 1. Herein, theorientation angle includes the roll angle Φ, the pitch angle θ, and theyaw angle φ. The major function of the orientation angle is to providethe relative angle or rotation relationship between the body frame ofthe writing device 1 and local level frame.

The roll angle Φ represents an angle that the writing device 1 rotatesalong a first axis of the body frame, which can be obtained byintegrating the angular velocity of the writing device 1 in the firstdirection. In other aspects, the roll angle Φ also represents an anglethat the writing device 1 rotates along the first direction, which canbe obtained according to the components of gravity measured by theaccelerometer of the writing device 1 in triaxial directions. Inaddition, the pitch angle θ represents an angle that the writing device1 rotates along a second axis of the body frame which can be obtained byintegrating the angular velocity of the writing device 1 in the seconddirection. In other aspects, the pitch angle θ also represents an anglethat the writing device 1 rotates along the second direction, which canbe obtained according to the components of gravity measured by theaccelerometer of the writing device 1 in triaxial directions. The yawangle φ represents an angle that the writing device 1 rotates along athird axis of the body frame which can be obtained by integrating theangular velocity of the writing device 1 in the third direction. Inother aspects, the yaw angle φ also represents an angle that the writingdevice 1 rotates along the third direction, which can be obtainedaccording to the magnetic-field intensity measured by the magnetometerof the writing device 1, or by the geomagnetic orientation measured bythe electronic compass. Otherwise, the roll angle, pitch angle, and yawangle can also be obtained according to, for example but not limited to,the magnetic-field intensity, geomagnetic orientation, or theircombinations of the writing device 1.

Afterwards, the orientation transformation unit generates a coordinatetransformation matrix according to the angular velocity signal and itsorientation angle, so that the acceleration signals in three axesgenerated by the moving trajectory sensing module can be transformedfrom the body frame of the writing device 1 to the local level frame bythe coordinate transformation matrix. In addition, a gravitycompensation unit of the orientation calculation module performs agravity compensation to the acceleration signal so as to eliminate theacceleration variation caused by gravity. Then, a detecting-calibrationunit of the orientation calculation module calibrates the movingtrajectory. To be noted, the above-mentioned coordinate transformationand gravity compensation are well known by those who skilled in the art,so their detailed descriptions will be omitted.

With reference to FIG. 2A, for example, the user operates the writingdevice 1 to write a number “4”. A part of the moving trajectory from theposition A to the position B of FIG. 2A is generated as the writingdevice 1 is lifted up and moved. In this case, the moving trajectorycalibration method of the invention can perform a trajectory calibrationso as to eliminate the part of the moving trajectory generated as thewriting device 1 is lifted up and moved (from the position A to theposition B), thereby obtaining the correct moving trajectory of thenumber “4” as shown in FIG. 2B.

FIG. 1C is a flow chart of a moving trajectory calibration methodaccording to a preferred embodiment of the invention.

Referring to FIGS. 1B and 1C, the moving trajectory calibration methodis applied to receive a moving trajectory signal generated by a writingdevice 1 while moving on a written plane P. The preprocessing procedureof the moving trajectory signal has been described hereinabove, so thedetailed description thereof will be omitted.

FIG. 3A is a waveform diagram showing the acceleration signals in thefirst axis X, the second axis Y, and the third axis Z of the body frame,which are obtained from the moving trajectory signal outputted by themoving trajectory sensing module and preprocessed, for example, bycalibration and filtering. FIG. 3B is a waveform diagram showing theacceleration signals in three axes of FIG. 3A processed by a coordinatetransformation, wherein the acceleration signals are transformed fromthe body frame to the local level frame. As shown in FIG. 3B, the basiclevel in the third axis Z is 1 g, and the basic levels in the first axisX and the second axis Y are 0 g. In addition, FIG. 3C is a waveformdiagram showing the acceleration signals in three axes of FIG. 3Bprocessed by a gravity compensation. As shown in FIG. 3C, the gravitycompensation unit can perform a proper compensation to the accelerationsignals of the local level frame so as to eliminate the interference ofthe acceleration caused by gravity. Referring to FIG. 3C, the basiclevel in the first axis X, the second axis Y, and the third axis Z are 0g.

FIG. 1C is a flow chart of a moving trajectory calibration methodaccording to a preferred embodiment of the invention, wherein the movingtrajectory calibration method include the following steps P01 to P03.

First, the step P01 is to generate a first axial signal, a second axialsignal and a third axial signal according to the moving trajectorysignal by a detecting-calibration unit of an orientation calculationmodule, wherein the written plane P is composed of the first axis andthe second axis, and the third axis is perpendicular to the writtenplane P. In this embodiment, the first axis, the second axis, and thethird axis are three axes of the local level frame, which areperpendicular to each other (the axes X, Y and Z of FIG. 2A). Thewritten plane P is composed of the first axis X and the second axis Y,and the third axis Z is perpendicular to the written plane P. The firstaxial signal, the second axial signal, and the third axial signal(acceleration signals) are shown in FIGS. 4A to 4C, respectively. Inother embodiments, when the written plane is a vertical plane, such asthe plane composed of the axis X and axis Z of FIG. 2A, the third axisis the axis Y.

Next, the step P02 is to calibrate the first axial signal according tothe third axial signal by the detecting-calibration unit, so as togenerate a first axial trajectory signal. In this embodiment, the thirdaxial signal is caused by the motion of lifting up the writing deviceand moving the writing device to next stroke, so that it can be used tocalibrate the first axial signal and the second axial signal. Inaddition, the step P02 of calibrating the first axial signal furtherincludes: when a variation of the third axial signal within a timeinterval exceeds a preset signal value, the detecting-calibration unitzeros the first axial signal within the time interval. In other words,it is determined that the third axial signal is caused by the motion oflifting up the writing device and moving the writing device to nextstroke, so that the third axial signal is unnecessary. In more detailed,when the variation of the third axial signal within a time interval(between t1 and t2 of FIG. 4C) exceeds the preset signal value, it isdetermined that the third axial signal is caused by the motion oflifting up the writing device and moving the writing device to nextstroke. Thus, the signal in the first axis X within this time intervalmust be eliminated, which is to zero the first axial signal within thistime interval. FIG. 4A shows the first axial signal within this timeinterval but does not show that the first axial signal is zeroed withinthis time interval. Herein, the preset signal value can be defined bythe user.

Finally, the step P03 is to calibrate the second axial signal accordingto the third axial signal by the detecting-calibration unit, so as togenerate a second axial trajectory signal. Similarly, when a variationof the third axial signal within a time interval exceeds a preset signalvalue, the detecting-calibration unit zeros the second axial signalwithin the time interval. Thus, the signal in the second axis Y withinthis time interval must be eliminated too, which is to zero the secondaxial signal within this time interval. FIG. 4B shows the second axialsignal within this time interval but does not show that the second axialsignal is zeroed within this time interval. To be noted, the above orderof the steps P02 and P03 is for illustration only and is not to limitthe present invention. It is possible to perform the step P03 before thestep P02, or to perform the steps P02 and P03 at the same time.

FIG. 5A is a flow chart of a moving trajectory generation methodaccording to a preferred embodiment of the invention, and FIG. 5B is ablock diagram of the writing device applied to the moving trajectorygeneration method of FIG. 5A.

Referring to FIGS. 5A and 5B, the moving trajectory generation methodcomprises the steps of: sensing a moving trajectory while a writingdevice 1 moves on a written plane P by a moving trajectory sensingmodule of the writing device 1, and generating a moving trajectorysignal (step S01); generating a first axial signal, a second axialsignal, and a third axial signal according to the moving trajectorysignal by a detecting-calibration unit of an orientation calculationmodule, wherein the written plane P is composed of the first axis andthe second axis, and the third axis is perpendicular to the writtenplane P (step S02); and calibrating the first axial signal and thesecond axial signal according to the third axial signal by thedetecting-calibration unit, so as to generate a first axial trajectorysignal and a second axial trajectory signal (step S03). The step S01 hasbeen described hereinabove and the steps S02 and S03 can be referred tothe above steps P01 to P03, so their detailed descriptions will beomitted.

In addition, the moving trajectory generation method may furthercomprise a step of: displaying the calibrated moving trajectory by adisplay module according to the first axial trajectory signal and thesecond axial trajectory signal (step S04). In other words, as shown inFIG. 2B, a monitor of a computer can display the calibrated correctmoving trajectory. In this embodiment, as shown in FIG. 2B, theacceleration signal in the third axis Z caused by the motion of liftingup the writing device or moving the writing device to next stroke isremoved from the first axial signal and the second axial signal, so thatthe display module can display the calibrated moving trajectoryaccording to the first axial trajectory signal and the second axialtrajectory signal. To be noted, before the step S04, the movingtrajectory generation method further comprises the step of: performing acalculation to the first axial trajectory signal and the second axialtrajectory signal by a trajectory calculation unit of the orientationcalculation module (see FIG. 5B). In this step S04, the calibratedacceleration signals in the first axis and the second axis areintegrated twice to generate a displacement signal, and then thedisplacement signal is transformed to the moving trajectory which isdisplayed by the display module.

The other technical features of the moving trajectory generation methodhave been described in the above description, so they will be omittedhere.

FIG. 6A is a schematic diagram showing the moving trajectory as usingthe writing device 1 to write “12”, and FIG. 6B is a schematic diagramshowing a modified moving trajectory by applying the moving trajectorygeneration method of the invention to the moving trajectory of FIG. 6A,which is displayed by the display module. FIG. 7A is a schematic diagramshowing the moving trajectory as using the writing device 1 to write“86”, and FIG. 7B is a schematic diagram showing a modified movingtrajectory by applying the moving trajectory generation method of theinvention to the moving trajectory of FIG. 7A, which is displayed by thedisplay module.

As shown in FIGS. 6A and 7A, a part of the moving trajectory between thepositions A and B is caused by the motion of lifting up the writingdevice or moving the writing device to next stroke. Accordingly, asshown in FIGS. 6B and 7B, the moving trajectory generation method of theinvention can detect handwriting signals and correct the distortedmoving trajectory caused by the motion of lifting up the writing deviceor moving the writing device to next stroke, thereby obtaining thecorrect moving trajectory.

To sum up, in the moving trajectory calibration method and movingtrajectory generation method of the invention, a detecting-calibrationunit of an orientation calculation module generates a first axialsignal, a second axial signal, and a third axial signal according to themoving trajectory signal, while the written plane is composed of thefirst axis and the second axis, and the third axis is perpendicular tothe written plane. In addition, the detecting-calibration unitcalibrates the first axial signal and the second axial signal accordingto the third axial signal so as to generate a first axial trajectorysignal and a second axial trajectory signal, respectively, and thedisplay module then displays the calibrated moving trajectory accordingto the first axial trajectory signal and the second axial trajectorysignal. Accordingly, the moving trajectory calibration method and movingtrajectory generation method of the invention can detect handwritingsignals and correct the distorted moving trajectory as the writingdevice is lifted up or moved to next stroke so as to obtain the correctmoving trajectory.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiments, as well asalternative embodiments, will be apparent to persons skilled in the art.It is, therefore, contemplated that the appended claims will cover allmodifications that fall within the true scope of the invention.

1. A moving trajectory calibration method, which is applied to receive amoving trajectory signal generated by a writing device while moving on awritten plane, the calibration method comprising the steps of:generating a first axial signal, a second axial signal, and a thirdaxial signal according to the moving trajectory signal by adetecting-calibration unit of an orientation calculation module, whereinthe written plane is composed of a first axis and a second axis, and athird axis is perpendicular to the written plane; calibrating the firstaxial signal according to the third axial signal by thedetecting-calibration unit, so as to generate a first axial trajectorysignal; and calibrating the second axial signal according to the thirdaxial signal by the detecting-calibration unit, so as to generate asecond axial trajectory signal.
 2. The calibration method of claim 1,wherein the moving trajectory signal comprises an angular velocitysignal, an acceleration signal, a magnetic-field intensity signal, ageomagnetic orientation signal, or their combinations in three axes withrespect to a moving trajectory at different time points.
 3. Thecalibration method of claim 1, wherein the first axis, the second axis,and the third axis are perpendicular to one another.
 4. The calibrationmethod of claim 1, wherein the step of calibrating the first axialsignal further comprises: when a variation of the third axial signalwithin a time interval exceeds a preset signal value, thedetecting-calibration unit zeros the first axial signal within the timeinterval.
 5. The calibration method of claim 1, wherein the step ofcalibrating the second axial signal further comprises: when a variationof the third axial signal within a time interval exceeds a preset signalvalue, the detecting-calibration unit zeros the second axial signalwithin the time interval.
 6. A moving trajectory generation method,comprising the steps of: sensing a moving trajectory while a writingdevice moves on a written plane by a moving trajectory sensing module ofthe writing device, and generating a moving trajectory signal;generating a first axial signal, a second axial signal, and a thirdaxial signal according to the moving trajectory signal by adetecting-calibration unit of an orientation calculation module, whereinthe written plane is composed of a first axis and a second axis, and athird axis is perpendicular to the written plane; calibrating the firstaxial signal and the second axial signal according to the third axialsignal by the detecting-calibration unit, so as to generate a firstaxial trajectory signal and a second axial trajectory signal; anddisplaying the calibrated moving trajectory by a display moduleaccording to the first axial trajectory signal and the second axialtrajectory signal.
 7. The generation method of claim 6, wherein themoving trajectory signal comprises an angular velocity signal, anacceleration signal, a magnetic-field intensity signal, a geomagneticorientation signal, or their combinations in three axes with respect toa moving trajectory at different time points.
 8. The generation methodof claim 7, further comprising the step of: generating a coordinatetransformation matrix according to the angular velocity signal by anorientation transformation unit of the orientation calculation module,and performing a coordinate transformation to the acceleration signalsaccording to the coordinate transformation matrix.
 9. The generationmethod of claim 8, wherein the orientation transformation unitintegrates the angular velocity signal to obtain an orientation angle soas to generate the coordinate transformation matrix, and transforms theacceleration signals with the coordinate transformation matrix so as totransform the acceleration signals from a body frame of the writingdevice to a local level frame.
 10. The generation method of claim 9,further comprising the step of: performing a gravity compensation to theacceleration signal in the local level frame by a gravity compensationunit of the orientation calculation module.
 11. The generation method ofclaim 6, wherein the step of calibrating the first axial signal furthercomprises: when a variation of the third axial signal within a timeinterval exceeds a preset signal value, the detecting-calibration unitzeros the first axial signal within the time interval.
 12. Thegeneration method of claim 6, wherein the step of calibrating the secondaxial signal further comprises: when a variation of the third axialsignal within a time interval exceeds a preset signal value, thedetecting-calibration unit zeros the second axial signal within the timeinterval.
 13. The generation method of claim 6, further comprising thestep of: performing a calculation to the first axial trajectory signaland the second axial trajectory signal by a trajectory calculation unitof the orientation calculation module.
 14. The generation method ofclaim 6, wherein the written plane comprises a horizontal plane, avertical plane, or a slant plane.